Abstract
Age determination of Mytilus galloprovincialis Lamarck was done by a light penetration method. As the shells of this species are applied to penetrating light, a striped pattern is recognized by bands through which the light can and cannot pass. The latter portions are formed in the summer and autumn, while the light passable portions are formed in the spring. The number of light transmittable bands coincides with the age of the shell. The boundaries between these two kinds are very clear. Along these boundaries, the so-called "annual rings", which are formed in the winter exist. By applying the light penetration method together with annual winter rings count the age of the mussel can be precisely determined.
